The use of lithium titanate Oxide (LTO) batteries with supercapacitors in micro- and mild hybrid vehicles has been studied. The study involves vehicle simulations and laboratory tests of carbon/carbon supercapacitors and 20Ah LTO cells from EIG, Korea. Cycle testing of the LTO cells/module on a cycle to simulate their use with supercapacitors indicated that their charge acceptance was excellent even at a charging power of 2000W (500W/cell). The test data indicated that the LTO battery would be an excellent choice for micro-hybrid applications. Simulations of micro- and mild hybrid vehicle operation have been run using lead-acid and EIG LTO battery technologies in 16V and 48V system. It is clear from the results that the LTO batteries can function well in both the micro- and mild hybrids. The LTO batteries are much smaller than the lead-acid batteries and are more efficient. The LTO batteries had an efficiency of 95-97% while the lead-acid batteries had an efficiency of 85-88%. The effect on fuel economy of the higher efficiency of the LTO batteries was not significant for either the FUDS or highway driving cycle. This was true for even the accessory load of 800W

Burke, Andrew

Zhao, Jingyuan

eScholarship - University of California

UC DavisResearch ReportsTitleSupercapacitors in Micro- and Mild Hybrids with Lithium Titanate Oxide Batteries: Vehicle Simulations and Laboratory TestsPermalinkhttps://escholarship.org/uc/item/87j1k9fnAuthorsBurke, AndrewZhao, JingyuanPublication Date2015-12-01eScholarship.org Powered by the California Digital LibraryUniversity of California  Institute of Transportation Studies ◦ University of California, Davis 1605 Tilia Street ◦ Davis, California 95616 PHONE (530) 752-6548 ◦ FAX (530) 752-6572 www.its.ucdavis.edu   Research Report – UCD-ITS-RR-15-20     Supercapacitors in Micro- and Mild Hybrids with Lithium Titanate Oxide Batteries: Vehicle Simulations and Laboratory Tests   December 2015    Andrew Burke Jingyuan Zhao EEVC - European Electric Vehicle Congress  1European Battery, Hybrid and Fuel Cell Electric Vehicle Congress Brussels, Belgium, 2nd - 4th December 2015 Supercapacitors in Micro- and Mild Hybrids with Lithium Titanate Oxide Batteries: Vehicle Simulations and Laboratory Tests Andrew Burke, Jingyuan Zhao Institute of Transportation Studies University of California-Davis, California 95616 USA Abstract The use of lithium titanate Oxide (LTO) batteries with supercapacitors in micro- and mild hybrid vehicles has been studied. The study involves vehicle simulations and laboratory tests of carbon/carbon supercapacitors and 20Ah LTO cells from EIG, Korea.  Cycle testing of the LTO cells/module on a cycle to simulate their use with supercapacitors indicated that their charge acceptance was excellent even at a charging power of 2000W (500W/cell).  The test data indicated that the LTO battery would be an excellent choice for micro-hybrid applications. Simulations of micro- and mild hybrid vehicle operation have been run using lead-acid and EIG LTO battery technologies in 16V and 48V system.  It is clear from the results that the LTO batteries can function well in both the micro- and mild hybrids.  The LTO batteries are much smaller than the lead-acid batteries and are more efficient.  The LTO batteries had an efficiency of 95-97% while the lead-acid batteries had an efficiency of 85-88%.  The effect on fuel economy of the higher efficiency of the LTO batteries was not significant for either the FUDS or highway driving cycle.  This was true for even the accessory load of 800W.   Keywords: supercapacitor, battery, hybrid vehicle, simulation, fuel economy1 Introduction The mass marketing of micro-hybrid passenger cars is well underway around the world.  In most cases, specially designed lead-acid batteries are used and the engine is turned off when the vehicle stops as long as the battery can accept the recharge in a reasonable [x].  Unfortunately the charge acceptance of the lead-acid battery degrades in a relatively short time and the stop-go feature of the vehicles stops working.  There are a several auto manufacturers [x] who have begun to use supercapacitors with the lead-acid batteries.  The supercapacitors perform the engine starting function at all times and provide the accessory load when the vehicle stops are short.  This approach has been found to significantly extend the life of the lead-acid battery.  Other auto manufacturers are considering the use of lithium batteries in place of the lead-acid battery in stop-go micro-hybrids.  The lithium ion battery must have high power and long life.  Likely the best lithium chemistry for this application is the lithium titanate oxide (LTO) battery.  The USABC has funded a project [x] to develop a LTO battery for the stop-go application.  The study reported in this paper involves consideration of various aspects of the application of LTO batteries with supercapacitors in stop-go hybrid vehicles.  The batteries used in the study are 6Ah and 20Ah cells from EIG in Korea.   2 Testing of EIG lithium titanate oxide batteries (LTO) EIG, Korea provided 6Ah and 20Ah cells to UC Davis for testing for use in hybrid vehicle EEVC - European Electric Vehicle Congress  2applications.  The  6Ah cells would be used in high voltage applications and the 20Ah cells would be used in 12V systems.  The cells were tested at constant current and constant power and in pulse test to determine their resistance. The results of the tests are shown in Table 1 and 2.  The 6Ah cells are high power cells (1075  W/kg)95% ) with a relatively low energy density of 40 Wh/kg.  The 20Ah cells have a higher energy density (70 Wh/kg), but lower power density capacity (381 W/kg)95%)  than the 6 Ah cells.  Both cells will  have excellent charge acceptance capability and long cycle life [x].  The 20Ah cells were further tested for the 12V micro-hybrid application and the characteristics of both cells were used in simulations of hybrid vehicles to be discussed later in the paper. Table 1: EIG cell 6Ah LTO cell  Constant Current test Discharge current Ah Time(sec) Resistance mOhm 2A 6.05 10891.7  3A 6.00 7204.9  6A 5.71 3425.1  12A 5.42 1625.1  30A 5.18 621.5  60A 4.90 294.1 1.0 80A 4.80 217.5 .875 Weight  .276 kg  Constant Power test Discharge power Time  (sec) Wh Energy density   Wh/kg Power density W/kg 10w 2166.6 11.4 41.7 36.3 20w 1396.4 10.6 38.6 72.7 30w 1042.1 10. 37.9 109.0 60w 565.4 9.3 33.9 218.1 90w 388.8 8.0 29.2 327.2 120w 287.1 6.8 24.7 436.3 200w 169.2 4.3 15.8 727.2 Calculation of the 95% efficient pulse power: P = .95 x .05 x (2.5)2 /.001 = 297W,  297/.276 = 1075 W/kg   Table 2:  UC Davis test data for the EIG 20 Ah LTO cell Constant current  A Ah Resistance  mOhm  75% SOC 4 20.9  10 20.9  20 20.7  40 20.5  100 20.3 1.2 200 20.1 1.2  Constant power W W/kg Wh Wh/kg 20 31 50.3 77.5 30 46 48.6 75.0 50 77 47.3 73.0 100 154 47.2 72.8 200 309 45.6 70.4 300 463 43.3 66.8 400 617 41.2 63.6  Cell weight   .648 kg  Calculation of the 95% efficient pulse power:  P = .95 x .05 x (2.5)2 /.0012 = 247W,  247/.648 = 381 W/kg  EEVC - European Electric Vehicle Congress  33 Testing of advanced carbon/carbon supercapacitors Carbon/carbon supercapacitors with energy and power capability better than those commercially available from Maxwell and Ness (4.2 Wh/kg, 1000 W/kg 95% )  have been tested at UC Davis [1].  The more advanced devices were developed by Skeleton Technologies in Estonia and Yunasko in Ukraine.  The characteristics of the advanced devices based on UC Davis test data are given in Tables 3 and 4. Table 3: Skeleton 3200F Device characteristics                Carbon/carbon with graphene, acetronitrile   3.4V   Packaged Weight 400 gm, volume 284 cm3 Constant current discharge data  Current A Time sec Capacitance F Resistance mOhm  Steady-state R RC sec 50 107.7 3205   100 52.7 3175   200 25.5 3178 .475 1.51 300 16.5 3173 .467 1.48 350 14 3202 .485 1.55 400 12 3168 .468 1.48 Discharge 3.4V to 1.7V; Resistance calculated from extrapolation of the voltage to t=0 Capacitance calculated from C= I*t disch/ delta from Vt=0  Constant power discharge data                                                                                      Power W W/kg Time sec Wh Wh/kg Wh/L 106 265 123.1 3.62 9.05 12.8 201 503 64.9 3.62 9.05 12.8 301 753 42.4 3.55 8.88 12.5 400 1000 31.1 3.46 8.65 12.2 500 1250 24.3 3.38 8.45 11.9 600 1500 19.8 3.3 8.25 11.6 Pulse power at 95% efficiency: P = 9/16 (1- eff) VR2/Rss ,  (W/kg)95% = 1730,  (W/L)95% = 2436 Matched impedance power: P= VR2 / 4 Rss , (W/kg) = 15, 400  Table 4: Yunasko 1200F Supercapacitor Constant current discharge data    2.75 – 1.35V Current A Time sec Capacitance F Steady-state Resistance mOhm 30 57.3 1273 -- 60 29.1 1293 --- 100 17.8 1290 --- 150 12.0 1281 .10 250 7.15 1276 .08 300 5.8 1261 .10 350 5.0 1268 .11                       Constant power discharges data    2.75 – 1.35V  Power  W W/kg * Time sec Wh Wh/kg 44 200 79.8 .975 4.43 72 327 51.0 1.02 4.64 102 464 35.6 1.01 4.59 152 690 24.0 1.01 4.59 200 909 18.1 1.01 4.59 250 1136 14.5 1.01 4.59 300 1364 12.0 1.00 4.55 350 1591 10.3 1.00 4.55 400 1818 9.0 1.00 4.55 * weight of device  -  .220 kg as tested EEVC - European Electric Vehicle Congress  4 Constant power discharge data                                                                                      Power W W/kg Time sec Wh Wh/kg Wh/L 106 265 123.1 3.62 9.05 12.8 201 503 64.9 3.62 9.05 12.8 301 753 42.4 3.55 8.88 12.5 400 1000 31.1 3.46 8.65 12.2 500 1250 24.3 3.38 8.45 11.9 600 1500 19.8 3.3 8.25 11.6 Pulse power at 95% efficiency: P = 9/16 (1- eff) VR2/Rss ,  (W/kg)95% = 1730,  (W/L)95% = 2436 Matched impedance power: P= VR2 / 4 Rss , (W/kg) = 15, 400                      P=9/16 x (1- eff) V0 2 /R = 9/16 x (.05) (2.75)2 /.00011 = 1934W                   (W/kg) 95% packaged =1934/.22 = 8791, 11,868 W/L   Device  V rated  C (F)  R mOhm  RC sec  Wh/kg  W/kg (95%) W/kg Match. Imped.  Wgt (kg)  Vol. (L) Yunasko 2.75 1275 0.11 0.14 4.55 8791 78125 .22 .163   Table 5: Yunasko 16V module  ( 6 x 1200F cells) Constant current discharge data   16.2-8.1 V  Current A  Time sec  Capacitance F Steady-state Resistance mOhm 10 168 207  25 67 207  50 33 205  100 16 201 .5 150 11 208 .8 200 8 204 .3      Constant power discharges data    16.2-8.1 V  Power  W W/kg * Time sec Wh Wh/kg * 157 127 126 5.5 4.4 300 240 65 5.42 4.34 450 360 43.5 5.44 4.35 600 480 32.4 5.40 4.32 900 720 21.4 5.35 4.28 1500 1200 12.6 5.25 4.2 2000 1600 9.3 5.17 4.14 * cell weight  -  1.25 kg   The supercapacitor from Skeleton has a higher energy density by a factor of two than the commercial devices and also higher by nearly a factor of two.  Hence it is well suited for hybrid vehicle applications.  The device from Yunasko has very high power – nearly a factor of 10 higher than the commercial devices.  Its energy density is about the same as the commercial devices. The Yunasko devices have been assembled in a 16V module which has been tested at UC Davis.  The characteristics of the 16V module are given in Table 5.    The Yunasko 16V unit would be ideal for use in micro-hybrid, because its efficiency if very high and there would be very small loss as the energy is transferred to and from the components in the system. EEVC - European Electric Vehicle Congress  54 Cycle testing of LTO cells for micro-hybrid applications A detailed study of the use of supercapacitor with lead-acid batteries in micro-hybrid applications is discussed in [2, 3].  In that study, a test cycle was developed for cycling a lead-acid battery as if it will in a system with supercapacitors in a micro-hybrid vehicle.  That cycle was used to life cycle a lead-acid battery for micro-hybrid applications.  It was found that the charge acceptance of the lead-acid battery degraded rapidly over the 400 cycles of the test.  That test cycle was based on a vehicle accessory load of 500W and a battery charge power of 400W.  In a recent study [4] of 12V battery requirements for start-stop applications by NREL for the USABC, it was found that the accessory load should be 750W and the battery recharge power should be 2000W.  These test conditions were used in the present tests of batteries for micro-hybrid applications.  The test cycle used previously for the lead-acid battery and that used for the LTO battery based on the new information [4] are compared in Table 6.  The charge times for the lithium batteries were decreased compared those for the lead-acid battery to reflect the higher ability of the lithium batteries to accept charge.  Detailed cycle testing of a 12V Gel lead-acid battery using the cycle given in Table 6 is discussed in [3].  It was found that the lead-acid battery could not be recharged even at 400W after a relatively few cycles as shown in Figure 1.  The lead-acid battery meet the other parts of the cycle after several days of testing, but its charge acceptance characteristics were not suitable for the micro-hybrid application.   Cycle tests of the LTO lithium battery were made using both single cells and a 16V module consisting of six of the 20Ah cells (see Figure 2-3).  Both the cell and module were tested using the test cycle given in Table 6.  The module was cycle through 124 cycles and the cell was cycled through 400 cycles.  As shown in Figures 2-3, the charge acceptance of the LTO battery was excellent and the battery could be recharge at 2000W at all parts of the cycle.  The cell voltages remained below 2.8V and the variation between the cells was relatively small (less than 50mv in most cases). The difficulty encountered was providing the 3 kW to start the engine and maintaining a cell voltage greater than 1.5V.  On a cell basis, this power corresponds to 770 W/kg which is a high value for this battery.  The LTO battery seems well suited for the micro-hybrid application, but it will require a higher power cell than the 20 Ah cell tested in this study.  Table 6: Battery test cycles for lead-acid and lithium batteries                                                 Lead-acid                                  Lithium  LTO Time (s) Step  Time(s) Step 40 0.5kW discharging  40 0.75kW discharging 1 3kW discharging Engine start  1-2 3kW discharging Engine start 5 Rest   5 Rest  32 0.4kW charging,    9 2.0kW charging,   42 Rest  42 Rest 41.4 0.4kW charging    11 2.0kW charging   85 Rest   85 Rest  11 0.5kW discharging  11 0.75 discharging 1 3kW discharging Engine start  1-2 3kW discharging Engine start 17 Rest   17 Rest  31.6 0.4kW charging    9 2.0kW charging   120 Rest   120 Rest  14 0.5kW discharging  14 0.75kW discharging 1  3kW discharging Engine start  1-2 3kW discharging Engine start 20 Charging to ∆Ah = 0   9 Charging to ∆Ah = 0  5 Rest    Rest  EEVC - European Electric Vehicle Congress  6   Figure 1:  Recharge voltage and power of the 12V Gel lead-acid battery at the end of the test cycle       Figure 2: Voltage at the end of a recharge step for the LTO module                Figure 3: Voltage at end of a recharge step for the LTO cell 5 Simulation results using LTO batteries in micro- and mild-hybrids  Simulations of micro- and mild hybrid vehicle operation have been run using lead-acid and EIG LTO battery technologies in 16V and 48V system.  Both systems used the batteries in combination with carbon/carbon supercapacitors.  The batteries provide the accessory and acceleration loads when the supercapacitors are depleted and need to be recharged from the engine.  The 16V system utilized a 4 kW electric motor and the 48V system used a 12 kW motor.  Both systems utilized a parallel hybrid configuration with a 120kW engine in the mid-size passenger car being simulated.  The accessory load of 400W or 800W was provided by the capacitors when the vehicle was stopped if their state-of-charge permitted: otherwise the accessory load was provided by the 13.51414.51515.50 100 200 300 400Voltage0.30.320.340.360.380.40 100 200 300 400Power15.415.615.81616.216.4cycle 714212835424956637077849198105112119VoltagecyclesLTO module cycling test in Micro‐HEV2.42.452.52.552.62.65cycle23466992115138161184207230253276299322345368391VoltageCyclesLTO cell cycling test in Micro‐HEVEEVC - European Electric Vehicle Congress  7batteries.  The results of the simulations are given in Table 7and Figures 4 and 5.  It is clear from the results that both the lead-acid and LTO batteries can function well in both the micro- and mild hybrids.  However, the LTO batteries are much smaller than the lead-acid batteries and more efficient.  The LTO batteries had an efficiency of 95-97% while the lead-acid batteries had an efficiency of 85-88%.  The effect on fuel economy of the higher efficiency of the LTO batteries was not significant for either the FUDS or highway driving cycle.  This was true for even the accessory load of 800W.  As expected the increase in fuel economy was greater for the mild-hybrid than for the micro-hybrid although it was significant for both hybrids.  Decisions on the battery type to use will depend to a large extent on the cycle life of the battery in the two hybrid applications.  Experience to date indicates that the lead-acid battery will not have satisfactory cycle life and the LTO battery will be the better choice.  It seems likely that both hybrid systems could function satisfactorily with only the LTO battery, but the battery will have to be larger than would be needed with supercapacitors. Table 7:  Hybrid vehicle simulation results using lead-acid and Lithium titanate oxide (LTO) batteries                Mid-size Passenger car: weight 1660 kg, CD =.3, Af =2.2m2 , fr =.009 Mild hybrid 48V Weight of caps kg Energy stored Wh Weight of the battery Energy stored  Wh FUDS Mpg* Highway Mpg* Lead-acid 13 50 38 950 37.7/35.1 45.7/44.9 LTO 13 50 6 240 38.1/34.9 46.3/45.2        Micro-hybrid  16V       Lead-acid 4 16 12 300 32.4/30.0 41.8/40.5 LTO 4 16 4 180 33.5/30.2 41.6/40.7        Conventional vehicle     26 37  * mpg  accessory load   400W/800W  Figure 4: 16V Micro-hybrid with LTO battery and Maxwell supercapacitors on the FUDS  EEVC - European Electric Vehicle Congress  8   Figure 5: 16V Micro-hybrid with lead-acid battery and Maxwell supercapacitors on the FUDS     6 Summary The use of lithium titanate Oxide (LTO) batteries with supercapacitors in micro- and mild hybrid vehicles has been studied.  The study involved vehicle simulations and laboratory tests of carbon/carbon supercapacitors and 20Ah LTO cells from EIG, Korea.  Test data are presented for advanced carbon/carbon supercapacitors from Skeleton Technologies, Estonia and Yunasko, Ukraine.  These supercapacitors are ideal for use in stop-go micro-hybrids with batteries.  The EIG LTO batteries had an energy density of 77 Wh/kg and modest power capability of about 400 (W/kg)95% pulse  .  Cycle testing of the LTO cells/module on a cycle to simulate their use with supercapacitors indicated that their charge acceptance was excellent even at a charging power of 2000W (500W/cell).  The test data indicated that the LTO battery would be an excellent choice for micro-hybrid applications. Simulations of micro- and mild hybrid vehicle operation were run using lead-acid and EIG LTO battery technologies in 16V and 48V system.  It is clear from the results that the LTO batteries can function well in both the micro- and mild hybrids.  The LTO batteries are much smaller than the lead-acid batteries and are more efficient.  The LTO batteries had an efficiency of 95-97% while the lead-acid batteries had an efficiency of 85-88%.  The effect on fuel economy of the higher efficiency of the LTO batteries was not significant for either the FUDS or highway driving cycle.  This was true for even the accessory load of 800W.  As expected the increase in fuel economy was greater for the mild-hybrid than for the micro-hybrid although it was significant for both hybrids.  Decisions on the battery type to use will depend to a large extent on the cycle life of the battery in the two hybrid applications.   EEVC - European Electric Vehicle Congress  9References [1] Burke, A.F., Supercapacitors (book edited by Francois Beguin and Elizbieta Frackowiak, published by Wiley-VCH, 2013), Chapter 12: Testing of Electrochemical Capacitors. [2] Burke, A.F., Miller, M., Zhao, H., Radenbaugh, M., and Liu, Z., Ultracapacitors in micro- and mild hybrid with lead-acid batteries: Simulations and laboratory and in-vehicle testing, Electric Vehicle Symposium 27, November 17-20, 2013, Barcelona, Spain [3] Liu. Zhengmao, The use of ultracapacitors in hybrid vehicles, Master of Science thesis, University of California-Davis, Institute of Transportation Studies, Dec. 2014 [4] Tataria, H., etals.,  USABC Development of 12 Volt Battery for Start-Stop Application, paper presented at EVS27, Barcelona, Spain, November 2013 

English

Supercapacitors in Micro- and Mild Hybrids with Lithium Titanate Oxide Batteries: Vehicle Simulations and Laboratory Tests

https://escholarship.org/content/qt87j1k9fn/qt87j1k9fn.pdf?t=pzet8e

Supercapacitors in Micro- and Mild Hybrids with Lithium Titanate Oxide Batteries: Vehicle Simulations and Laboratory Tests

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California